1. Field of the Invention
The present invention is related to a gas-circuit breaker installed in, for example, an electric-power substation and/or a switching station.
2. Description of the Related Art
A conventional gas-circuit breaker includes an arc-extinguishing chamber to extinguish an arc generated between contact. In such an arc-extinguishing chamber, a mechanical puffer is used to mechanically compress an arc-extinguishing gas (hereinafter, “gas”) and blow the compressed gas onto an arc. In recent years, a thermal puffer is used in combination with the mechanical puffer to increase the pressure of the gas by using the heat of the arc.
The conventional gas-circuit breaker, in which thermal puffer and mechanical puffer are used together, is disclosed in Japanese Patent Publication No. H07-109744. FIGS. 5 and 6 are a cross sections of the conventional gas-circuit breaker disclosed in Japanese Patent Publication No. H07-109744 in a closed position (current is flowing) state and in an open position (current is interrupted), respectively.
As shown in FIGS. 5 and 6, a gas-circuit breaker is housed in a container 230. The container 230, part of which is shown in the figure, is filled with a gas, for example, sulfur hexafluoride (SF6), used for extinguishing an arc. The gas-circuit breaker includes a stationary contact 210 that is fixed to a first side of the container 230, and a moving contact 220 that is capable of moving linearly on a central axis X, by an operating device (not shown). Because of such a movement, the moving contact 220 is capable of physically contacting or separating from the stationary contact 210.
The stationary contact 210 has a stationary arc-contact 211 arranged on the central axis X. The moving contact 220 includes a moving arc-contact 221, a thermal chamber 222, and a pressure chamber 223. The moving arc-contact 221 moves linearly along the axis X with respect to the stationary arc-contact 211, and it is capable of electrically contacting or separating from the stationary arc-contact 211.
The thermal chamber 222 is located between the moving arc-contact 221 and the pressure chamber 223, and moves linearly on the central axis X along with the moving arc-contact 221 with the operation of a hollow operating rod 224. The pressure chamber 223 is configured of a cylinder 225 that moves linearly along with the moving arc-contact 221 and the thermal chamber 222, and a stationary piston 226 that is supported by the container 230. Due to opening movement of the moving contact 220 (i.e., movement towards right in FIG. 5), the volume of the pressure chamber 223 decreases, whereby the gas inside is compressed.
The thermal chamber 222 has two vents. One vent 222a opens towards the moving arc-contact 221 and another vent 222b opens in the pressure chamber 223. A check valve 222c is located between the thermal chamber 222 and the pressure chamber 223 in the vent 222b. The check valve 222c opens when the pressure inside the pressure chamber 223 is higher than the pressure in the thermal chamber 222, whereby the gas flows from the pressure chamber 223 into the thermal chamber 222. On the contrary, the check valve 222c closes when the pressure in the thermal chamber 222 is higher than the pressure in the pressure chamber 223, thereby preventing flow of gas from the thermal chamber 222 into the pressure chamber 223.
Furthermore, a relief valve 223a is located on the stationary piston 226. At the time of current interruption, when the pressure in the pressure chamber 223 increases above a predetermined pressure, the relief valve 223a opens. When the relief valve 223a opens, the gas inside the pressure chamber 223 flows into the container 230 whereby the pressure in the pressure chamber 223 from increasing above the predetermined pressure.
In closed position (i.e., when current is flowing), the stationary contact 210 and the moving contact 220 are in electrical contact, so that current flows between the stationary contact 210 and the moving contact 220. At the time of current interruption, the moving contact 220 moves to the right in FIG. 5, separates from the stationary contact 210, and an arc is formed between the stationary arc-contact 211 and the moving arc-contact 221.
When the interruption current is large, the temperature of the gas in the thermal chamber 222 increases due to heat of the arc, and the gas expands, leading to increased pressure in the thermal chamber 222. If the pressure in the thermal chamber 222 is higher than pressure of compressed gas in the pressure chamber 223, the check valve 222c between the thermal chamber 222 and the pressure chamber 223 closes. As the current reduces and becomes closer to 0, the highly pressurized gas in the thermal chamber 222 blows onto the arc that is generated between the stationary arc-contact 211 and the moving arc-contact 221 through the vent 222a. Thus, the arc is quenched and electric current is interrupted.
On the other hand, when the interruption current is small, rise in the temperature in the thermal chamber 222 is smaller. As a result, the gas inside the pressure chamber 223 is compressed due to interruption, and the pressure in the pressure chamber 223 is higher than the pressure in the thermal chamber 222. Therefore, the check valve 222c between the thermal chamber 222 and the pressure chamber 223 opens. As a result, the highly pressurized gas in the pressure chamber 223 passes through the thermal chamber 222 and the vent 222a, and blows onto an arc that is generated between the stationary arc-contact 211 and the moving arc-contact 221 so that the current is interrupted.
Thus, in the conventional technology, large current interruption performance depends on the capacities of the thermal chamber 222 and the pressure chamber 223. Because it is necessary to locate the thermal chamber 222 between the moving arc-contact 221 of the moving contact 220 and the pressure chamber 223, it is necessary to secure space between the stationary contact 210 and the stationary piston 226 proportionate to the capacity of the thermal chamber 222, in addition to the operation stroke of the moving contact 220.
Therefore, when the capacity of the thermal chamber 222 is increased along with the increase in the interruption current, the gas-circuit breaker becomes lengthy along the axis, and it is not possible to downsize the gas-circuit breaker. Furthermore, when the interruption current is smaller, even if the capacity of the pressure chamber 223 is reduced, space in the thermal chamber 222 becomes a dead space, and pressure of the gas cannot be increased.